Production and isolation of lactic acid using thermophilic bacteria Bacillus smithii DSM 460

Održiva upotreba lignocelulozne biomase za dobivanje raznih biokemikalija, poput mliječne kiseline uključuje iskorištavanje svih ugljikohidrata prisutnih u njenim hidrolizatima. Zbog toga je važna upotreba mikroorganizama koji mogu koristiti pentoze i heksoze kako bi proces bio ekonomičan. Cilj ovog rada bio je odrediti optimalne uvjete za proizvodnju mliječne kiseline pomoću bakterije Bacillus smithii DSM 460, u svrhu dobivanja što većeg prinosa proizvoda u različitim bioreaktorskim sustavima. Također je istražena i mogućnost izolacije mliječne kiseline iz fermentirane podloge pomoću adsorpcijske smole. Iz provedenog istraživanja najveće koncentracije mliječne kiseline se postižu u bioreaktoru s miješalom (približno 28 g Lˉ¹) pri temperaturi od 55°C uz koeficijent konverzije supstrata u mliječnu kiselinu preko 90 % teoretske vrijednosti. Tijekom uzgoja provedenom pri temperaturi od 45°C u istim uvjetima postiže se oko 40 % manja koncentracija mliječne kiseline (≈ 17 g Lˉ¹). Utjecaj temperature zanemariv je na odvijanje procesa adsorpcije, a najveći kapacitet postignut je pri 40°C (0,2480 g mliječne kiseline/g vlažne smole).Sustainable use of lignocellulosic biomass to produce a variety of biochemicals, such as lactic acid involves the utilization of all carbohydrates present in its hydrolysates. Therefore, it is important to use microorganisms that can use pentoses and hexoses to make the process economical. The aim of this study was to determine the optimal conditions for the production of lactic acid using the bacterium Bacillus smithii DSM 460, in order to obtain the highest possible product yield in different bioreactor systems. The possibility of isolating lactic acid from a fermented medium using an adsorption resin was also investigated. From the performed research, the highest concentrations of lactic acid were achieved in a bioreactor with a stirrer (approximately 28 g Lˉ¹) at 55 °C with a coefficient of conversion of the substrate into lactic acid over 90 % of the theoretical value. During cultivation at 45 °C in the same conditions, about 40 % lower concentration of lactic acid (≈ 17 g Lˉ¹) was achieved. The influence of temperature is negligible on the adsorption process, and the highest capacity was achieved at 40°C (0,2480 g of lactic acid / g of wet resin)